1. Field of the Invention
This invention relates to novel thermoplastic resin compositions consisting essentially of a specific methacrylimide-containing polymer, a polyester and a polycarbonate. More particularly, it relates to thermo-plastic resin compositions consisting essentially of the aforesaid three components and having excellent mechanical properties and moldability.
2. Description of the Prior Art
While methacrylimide-containing polymers have a high heat distortion temperature and excellent properties such as stiffness, surface hardness and moldability, they are poor in mechanical strength as typified by impact strength. Thus, as long as methacrylimied-containing polymers are used alone, their use as molding materials is rather limited under the existing circumstances.
Thermoplastic polyesters, as typified by polyethylene terephthalate and polybutylene terephthalate, have excellent mechanical properties, chemical resistance and electrical characteristics and are being used in wide applications including electrical and electronic equipment parts, automobile parts and the like. However, because of their low heat distortion temperatures under high load (as measured according to ASTM D-648 under a load of 18.56 kg/cm.sup.2), they cannot be used as structural materials which may be subjected to high loads under high-temperature conditions. Moreover, since they are crystalline polymers and exhibit high molding shrinkage, difficulties are encountered in molding them.
Polycarbonate resins are excellent in mechanical properties as represented by thermal resistance and impact resistance, but poor in surface hardness and solvent resistance. Thus, their use is considerably limited in the existing circumstances.
The present inventors have made an intensive study with a view to improving the mechanical properties of methacrylimide-containing polymers, the heat distortion temperature under high load and molding shrinkage of thermoplastic polyesters, and the surface hardness and solvent resistance of polycarbonate resins. As a result, it has been discovered that the combination a specific methacrylimide-containing polymer, a thermoplastic polyester and a polycarbonate resin provides resin compositions exhibiting good compatibility and having excellent mechanical properties, thermal resistance, surface hardness, solvent resistance and moldability. The present invention has been completed on the basis of this discovery.